As nonaqueous electrolyte secondary batteries using alkali metals such as lithium and sodium as the negative electrode, there has been up to date actively pursued the development of those batteries which use, as positive-electrode active material, various intercalation compounds and the like including titanium disulfide (TiS.sub.2) and, as electrolyte, organic electrolyte obtained by dissolving lithium perchlorate or the like in an organic solvent such as propylene carbonate. These secondary batteries are characterized by a high battery voltage and a high energy density owing to the use of alkali metals in the negative electrode.
However, the secondary batteries of this kind have not yet been put to practical use up to date. The main reason for this is that the number of times of possible charge-and-discharge is small (charge-and-discharge cycle life is short) and the charge-and-discharge efficiency in charge-and-discharge cycle is low. This is caused largely by deterioration of the negative electrode. The lithium negative electrode mainly used at present comprises plate-formed metallic lithium press-bonded to a screen-formed current collector formed of nickel or the like. During discharging stage, metallic lithium is dissolved into electrolyte as lithium ions. But, in charging stage, it is difficult to precipitate the lithium into plate form as before discharge. Rather, there occurs such phenomena that dendrite-like (aborescent) lithium is formed, which falls off breaking near the root, or the lithium precipitated in small-bead (moss-like) form and disconnects itself from the current collector. Consequently, the battery becomes incapable of being charged and discharged. Further, it often occurs that the dendrite-like metallic lithium thus formed penetrates the separator separating the positive electrode from the negative electrode and comes into contact with the positive electrode and cause a shortcircuit, which results in failure of function of the battery.
Various methods have been tried up to the present to obviate the defects of the negative electrode mentioned above. In general, there are reported methods which comprise altering the material of the negative-electrode current collector to improve its adhesion to the precipitating lithium or methods which comprise adding to the electrolyte an additive for preventing the formation of dendrite-like metal. But these methods are not always effective. As to alteration of the current collector material, it is effective for lithium precipitating directly onto the current collector material; but on further continuation of charge (precipitation), lithium comes to precipitate upon the precipitated lithium, whereby the effect of current collector material is lost. As to the additives, also, they are effective in the early stage of charge-and-discharge cycle; but with further repetition of the cycle, most of the additives decompose owing to oxidation-reduction or the like in the battery, thus losing their effectiveness.
More recently, it has been proposed to use an alloy with lithium as the negative electrode. A well known example is lithium-aluminum alloy. In this case, there is disadvantage in that, though a uniform alloy is formed for the time being, the uniformity disappears on repetition of charge and discharge and, particularly when the proportion of lithium is large, the electrode becomes fine-grained and disintegrates. Also, it has been proposed to use a solid solution of silver and alkali metal [Japanese Patent Application Kokai (Laid-open) No. 73860/81; U.S. Pat. Nos. 4,316,777 and 4,330,601]. In this case, it is described that no disintegration occurs as in the aluminum alloy; but only a small amount of lithium goes into alloy in sufficiently high speed, and sometimes metallic lithium precipitates without alloying itself; to avoid this, use of a porous body or the like has been recommended. Accordingly, the charge efficiency with a large current is poor; with alloys containing large amount of lithium, the pulverization caused by charge-and-discharge is gradually accelerated, resulting in sharp decrease in cycle life.
Further, there is an idea of using lithium-mercury alloy [Japanese Patent Application Kokai (Laid-open) No. 98,978/82]or that of using lithium-lead alloy [Japanese Patent Application Kokai (Laid-open) No. 141,869/82]. In the case of lithium-mercury alloy, however, the negative electrode changes into mercury metal in the form of liquid particles as the result of discharge, and cannot maintain the form of the electrode. In the case of lithium-lead alloy, the pulverization of the electrode due to charge-and-discharge is more severe than in silver solid solution.
Further, it is conceivable to use lithium-tin or lithium-tin-lead alloy. Also when these alloys are used, the pulverization of the alloy occurs with the increase of the amount of lithium incorporated into alloy by charging, which makes maintaining the form as an electrode impossible.
Thus, there has yet been found no negative electrode rechargeable in nonaqueous electrolyte which can be satisfactorily used in practice.